The invention relates to a hydraulic adjusting device according to the preamble of claim 1.
Such a hydraulic adjusting device, in the form of a hydraulic adjusting cylinder with a closed working chamber, is known from U.S. Pat. No. 3,293,994 A, isolated by a cylinder wall on the circumference thereof, and stationary end walls position in relation to the cylinder wall, as delimiting elements. An adjustment piston that can be displaced axially is received in the working chamber. The piston rod of the adjustment piston passes through one of the end walls, into the working chamber in a sealed manner. This end wall is disposed in a fixed position in relation to the cylinder wall, sealed via a pair of seals having an annular space located axially between the seals.
The end wall through which the piston rod passes encloses an annular space surrounding the piston rod, in which a cylindrical piston is located. This cylindrical piston is sealed off to the piston rod and to the end wall in each case, and is disposed such that it can be displaced axially, with a limitation to the distance thereof. This delimitation in relation to the end wall is obtained by axially spaced apart delimit stops provided on the end surface and lying at the end of the cylindrical piston. The cylindrical piston is supported via a spring assembly in the direction toward the stop delimiting the adjustment path of the cylindrical piston in the extension direction of the piston rod. This spring assembly lies in an annular space, encompassing the piston rod, which annular space has a variable volume that can be modified by the axial adjustment of the cylindrical piston, which annular space is delimited axially by the cylindrical piston and an end surface of the end wall through which the piston rod passes. This variable volume, radial inner annular space and the radial outer annular space lying between the seals form, in each case, a leakage accumulation chamber and are connected via transition channels that pass radially through the end wall.
The piston rod is provided with a stop in its actuation-side end region extending axially over the cylindrical piston, which in the retraction direction of the piston rod delimits its adjustment path in relation to the cylindrical piston, and when the piston rod is retracted, conveys the cylindrical piston against the adjustment force of the spring assembly toward the end surface of the end wall through which it passes.
The leakage accumulation chambers are connected to the working chamber via a spring loaded blocking valve assembly on a return channel that acts against the return direction toward the working chamber. The leakage that, regardless of the seals, on one hand between the end wall through which the piston rod passes and the cylinder wall, and on the other hand, between this end wall and the piston rod, manages to pass into the leakage accumulation chamber, is pumped back toward the working chamber by means of the cylindrical piston conveyed by the retracting piston rod, such that only one leakage path remains, formed by the displaceable, sealed guide, between the cylindrical piston and the piston rod.
In addition to such complex adjusting devices, simple adjusting devices, formed by a hydraulic adjustment cylinder having a sealed piston disposed in the cylinder that can be displaced longitudinally, with which the respective adjusting forces applied by the hydraulic compression of the piston are transferred outward via a piston rod, which is sealed in relation to the cylinder via a cylinder-side sealing assembly. For the most part, simple rod seals are used thereby for the sealing assembly. The use of more complex tandem seals is also known, which are designed to prevent leakage to the greatest possible extent, are also designed as recirculating seals to the working chamber.
Aside from the fact that such recirculating tandem sealing arrangements require a function-conditional axial movement between the elements delimiting the sealing gap as a leakage path for the recirculation effect that is strived for, such as that between the piston rod and cylinder, there are leakage paths that are not only between parts that are moved axially against one another, but also between rotating parts or parts that are connected to one another in a stationary manner. This may result, in particular with regard to environmental conditions that are critical to leakage, in the suppression of such leakages, or even the prevention of such leakages to the greatest possible extent, through appropriate measures with regard to their negative effects, even when these leakages are of an insignificant nature.
The invention addresses the object of presenting a structurally simple possibility, with respect to more complex adjusting devices, of the type outlined in the preamble of claim 1, in order to also eliminate leakages running over unavoidable leakage paths, without having a negative effect on the functioning of the adjusting device.
In accordance with the invention, a sealing assembly having a recirculating effect is disposed in hydraulic adjusting devices for this purpose, having moving parts sealed against one another along an axial guidance path, as delimiting elements to a working chamber in the guidance path forming a leakage path, and the recirculation effect of this sealing assembly is used in order to also recirculate leakages occurring in another manner in the device through the connection of the respective leakage paths, or from leakage accumulation chambers provided for these leakage paths, with the recirculating sealing assembly in the hydraulic circuit of the adjustment device.
The merging of such leakages toward the recirculating sealing assembly occurs via one or more transition channels, which, along with the recirculating sealing assembly, the leakage paths and leakage accumulation chambers are provided with a delimiting element assigned thereto, in the form of an integral, or installed component of the device. In particular, such a design is advantageous when, with a rotatable assembly of the adjusting device, this delimiting element is also assigned to the supply input necessary for supplying the working chamber.
With the adjusting device according to the invention, a pot-shaped cylindrical piston and a bowl-body having a central dome, covered by the cylindrical piston, are provided as the delimiting elements, such that the working chamber is formed axially between the pot-floor of the cylindrical piston and the central dome of the bowl-body. Such assemblies are particularly suited for adjusting devices that can be used in different manners with an unchanging fundamental construction.
The merging of the occurring leakages for a collective recirculation toward the working chamber, and thus toward the hydraulic circuit, via a recirculating sealing assembly, has proven to be functional, in particular when the conveyance of the leakage to the recirculating sealing assembly is supported by centrifugal force, or occurs, alternatively, via a gradient. This is also the case when such sealing assemblies, by means of which a supplementary suction effect is obtained, are used as the recirculating sealing assembly.
Sealing assemblies used in the framework of the invention having seals that are axially spaced apart from one another in the leakage path are, in particular, so-called tandem seals, wherein the axial space lying between the spaced apart seals serves as a leakage accumulation chamber, into which the transition channel(s) open(s).
The invention has proven to be particularly advantageous in conjunction with hydraulic, axial adjusting devices, in which a working chamber is delimited in terms of its volume change capacity via axially displaceable delimiting elements, and the delimiting elements, together with the working chamber form a rotational unit that is coaxial in relation to the displacement direction of the delimiting elements, to which the supply input for the working chamber is disposed in a rotational and sealed manner, such that the supply input can be fixed in position, thus disposed in a stationary manner, and as a result, stationary connections or line connections can also be provided in the hydraulic feed at the supply input.
This is the case, by way of example, with adjusting devices integrated in the hub of a fan wheel having radial fan blades supported in the hub on its circumference, which can be adjusted in terms of their angle of incidence via the adjusting device functioning as an actuator. The hub can be axially and non-rotatably connected to a central rotary drive thereby, thus, by way of example, to the crankshaft of an internal combustion engine, or used as an axial actuator for a transmission having gear elements that are to be adjusted axially in relation to one another, thus, in particular, for a variable speed drive having tapered rollers that are to be adjusted axially in relation to one another in terms of their spacing, or conical belt pulleys that are to be adjusted axially in relation to one another, as is the case, for example, with CVT gearings. When used in this manner, it is beneficial if the adjusting device is supported in a rotational and axially stationary manner in relation to a supporting structure via its bowl body, such that the axially adjustable cylindrical piston acts on the respective part that is to be axially adjusted.
Thus, a hydraulic adjusting device having a working chamber with a changing volume capacity is obtained with the invention, in which at least two leakage paths are collectively assigned to a delimiting element of the working chamber, and are at least partially delimited by this delimiting element, and in which a sealing assembly is provided in a leakage path running along an axial guidance path for this delimiting element, which is connected to the other leakage path via a transition channel running in the delimiting element, and which is designed as a recirculating sealing assembly on the working chamber.